1. Field of the Invention
The present invention generally relates to surgical cable systems and the like. More particularly, an embodiment of the invention relates to a method and apparatus for securing surgical cable around a portion of a human bone.
2. Description of the Related Art
Surgical cables are used in a variety of surgical procedures, some examples include: spine surgery; total hip arthroplasty; fracture fixation; closure of the sternum following open heart surgery; and oral/facial surgery to repair mandibular fractures. In these and other surgical procedures the cable may be used to set and secure bone portions in the proper orientation during the healing process.
Fractures of the vertebrae in the spinal column are very difficult to imrnobilize, often requiring the use of internal pins, cables and/or rods. One frequently used procedure involves wiring the fractured vertebra to one or more adjacent vertebrae to secure the vertebra in an ideal position for healing. Another method involves wiring the fractured vertebra to a rod that is similarly joined to other vertebrae. Both of these methods, as well as other techniques for spinal repair, rely on the use of cables which are secured around a portion of a vertebra.
A number of methods for encircling bone portions with surgical cables have been developed. Most of these techniques involve passing a cable around a portion of the bone and securing the cable in position using a crimp. Example of cabling apparatus and methods are illustrated in U.S. Pat. Nos. 4,966,600; 5,395,374; 5,415,658; 5,423,820, and 5,569,253. Each of these patents is incorporated by reference as if fully set forth herein.
The Acromed.TM. Cable System by Songer, as shown in U.S. Pat. No. 4,966,600, represents a cabling system that relies on the use of a metal crimp member to secure a cable in a loop. In one embodiment of the Acromed.TM. system a crimp member is affixed to one end of the cable. The cable may then be passed partially through a connector. The crimp member may inhibit the cable from passing entirely through the connector. The cable may then be looped around the bone portion and passed again through the connector. A tensioning device is used to tighten the cable around the bone portion, and another crimp member is applied to the portion of the wire extending out from the connector to fix the cable in position.
The Acromed.TM. system relies on crimp members to attempt to irreversibly secure the cable in position. This feature may present difficulties if a number of cables are used in series since it is often necessary to retighten some of the cables as other cables are added. To overcome this problem a double crimp technique is commonly used. In this technique the cable is passed through two crimp members before the cable is tensioned. After tensioning, the top crimp member may be affixed to the cable. When the cable becomes loosened, it may be re-tensioned and the lower crimp member affixed to the cable. The upper crimp member may be trimmed off after the second crimp member is fastened to the cable. A disadvantage of this approach is that the number of re-tensions that may be performed is determined by the number of crimp members attached to the cable before the initial tensioning. If additional re-tensioning is required after the last crimp member has been attached to the cable, the cable may need to be removed and a new cable attached.
An orthopedic cable apparatus manufactured by Danek Medical Inc., as shown in U.S. Pat. Nos. 5,395,374 and 5,423,820, appears to overcome these problems. The apparatus consists of three separate parts: a double-apertured L-shaped crimp; a cable clamp; and a tensioning tool. The Danek system affixes one end of the cable to the double-apertured L-shaped crimp. The cable is then looped around the bone portion and passed through the other aperture of the L-shaped crimp. The cable is then passed through a cable clamp, and further through a tensioner. The tensioning device is used to tighten the cable around the vertebra. Once the appropriate tension is achieved the cable clamp is tightened to temporarily fix the cable in position. Since the cable clamp acts as a non-permanent securing device, the user is free to re-tension the cable a number of times during use. When the user is finished, the cable is fixed into position by crimping the second crimp portion of the L-shaped crimp onto the cable. The Danek cabling system avoids the need for multiple crimps, as used by the Acromed.TM. system, however, it still relies on crimps to secure the cable in position.
A disadvantage to the use of crimps for securing a cable in position is that the crimps may be highly unreliable. The crimps are typically compressed by the user to affix them to the cable. However, it may be very difficult to control the percentage of deformation of the crimp such that a predictable and consistent amount of deformation may be produced. If the crimp is over deformed some of the cable strands may be sheared off, reducing the strength of the cable at the connection. Conversely, if the crimp is under deformed, the crimp may be incapable of preventing the cable from loosening after the procedure is finished.
Another problem encountered when using cable systems is that they force the cable into a specific position relative to the point where the cable crosses itself. In some cases there is an advantage for the ends of the cable to be in a parallel orientation. Such an orientation allows a minimal profile of the connector. A low profile width is generally desired to minimize sinus formation and soft tissue irritation. The parallel orientation may sometimes cause a sharp bend in the cable, thereby creating stress in the system. To overcome this stress it is desirable for the ends of the cable to be in a perpendicular orientation relative to each other.
The Acromed.TM. apparatus, as shown in U.S. Pat. No. 4,966,600, may be used in a number of ways in order to achieve the desired cable orientation. In one method the cable comprises a permanently looped eyelet end. The other end of the cable may be through the eyelet to form a loop in which the ends of the cable reoriented perpendicular fashion. In another method the ends of the cable may be held in a parallel orientation by using a special connector designed for this purpose. The Danek system, as shown in U.S. Pat. No. 5,569,253, is also designed for use with the ends of the cable in a parallel or perpendicular orientation. The Danek sytn relies on the use of specially designed connectors for each orientation. Neither the Acromed or the Danek systems describe a single connector which would allow the cable to be positioned in both a parallel and a perpendicular orientation.
The above mentioned methods and systems inadequately address, among other things, the need for an apparatus that allows re-tensioning of the cable, as well as multiple orientations of the cable. The devices abo rely on crimps affixed to the cables to hold the cable in place. As mentioned before, such crimps may be unreliable. It is therefore desirable that a cable system be derived that incorporates, in a single device, the ability to allow the cable to be re-tensioned, a non crimping securing mechanism, and multiple cable orientations.